hpram99

I've got my engine apart, I was bored today.

I stuck the spark plugs in the proper holes to measure how far from the surface they sit. It seems that they are set pretty far back. The leading is about 6mm back, and the trailing is about 10mm+ (I forgot exactly).
The trailing also has a tiny hole for the spark, It is probably very difficult for it to ignite correctly if it is that far back (am I wrong?)

Is there any possible reason for the spark plugs being so far back? or can I go and but some longer plugs?

p.s. I'm using the stock ngk plugs. this is an s5 engine.

duboisr

First check to see if a washer is stuck on the housing or if the plug has two washers on it . If not , do think about it . All the others are doing fine ,The high pressure gases will get to the spark . If the spark is in a very very turbulant high pressure area the spark can be blown out . Can you say missfire .

hpram99

so it's set back so it doesn't get 'blown out' ?

black_sunshine

I'm not getting on you, but I should point out that you cannot blow-out a spark; just as you cannot blow-out light or magnetism without an insulator. Now, the fuel and air mixture may experience "flame-out" but never a "spark-out." Only under the condition that the gap of the spark plug is filled with a better conductor (read: shorted out via a liquid). Think of an arc (TIG) welder. I have had a friend try to blow out the arc (spark) with an air compressor, and all he succeded in doing was making my metal burn (presence of oxygen).

They sit far back for a reason. They have to be cooled by the water (especially the leading) jacket. The trailing sparkplug has a smaller hole to reduce blow-by during combustion eliminating 2 problems:

1) Reduced chances of igniting the fresh intake charge on other side of the apex seal,

2) to avoid loss of power from blow by.

In theory, the trailing is supposed to "shoot-out" a flame from that small hole; it supposedly helps ignite the rich idle mixture more evenly. Note the word "supposedly."

Now, I've dealt with the trailing spark plug holes before. I did an experiment I drilled-out the trailing holes larger (approximately the same size as the leading). It accomplished absolutely nothing, so don't do it. I didn't get any detonation or anything like that, and power seemed to be good (I was using my butt-dyno), but when I tried starting it on a dead battery, I DID get an actual backfire (through the intake), though if it was related or not, I'll never know.

The tip of the trailing should be just at the end of the hole, right before the tiny hole begins. I don't remember how far back the leading was, so I'm not going to say.

hpram99

Wow, looks like you spent a little to much time modding your fc

Thanks a bunch

Jeff20B

iTrader: (13)

I've done a slight experiment on trailing and its effect on idle, power, low RPM, mid RPM, high RPM etc while driving. Trailing did nothing whether switched on or off. I think I heard a slight difference while floored driving up a steep grade, but I also have a loud exhaust. It seemed to make a high pitched extra sound, but it was so hard to discern from the rest of the sounds all around me, that I may have been imagining it. Then I had a friend switch it for me and we think it helped power while driving up the hill, but if there was a difference, it was so slight that we couldn't feel it.

By the way, I've got direct fire, so both leading plugs always fire at the same time. This takes the place of the trailing plugs quite well. It ignites the somewhat unburned stuff at the 'trailing' edge of the rotor face.

This idea works so well, I'm doing it on my 20B.